1. Field of the Invention
This invention relates to a biocatalyst-immobilizing carrier (hereinafter referred to as an immobilizing carrier) wherein at least one biocatalyst such as an enzyme, a microbe or the like is stably immobilized in a carrier gel with the high activity of the catalyst being retained. More particularly, the present invention relates to a novel immobilizing carrier which can be utilized in such applications as (1) bioreactors for production of chemical substances, (2) biosensors for detection of chemical substances and (3) formation of color pattern or image utilizing a reaction by an organism such as an enzyme, a microbe or the like, as well as to a method for preparing an immobilized carrier.
2. Related Background Art
Techniques for biocatalyst immobilization are prerequisite as a basic technique for the development of biosensors or bioreactors, and researches on these techniques are actively under way throughout the world.
Reactions by a biocatalyst such as an enzyme, a microbe or the like, as compared with chemical reactions used in conventional chemical industrial processes, have the following advantages.
(1) Reactions proceed at a normal temperature and a normal pressure, giving energy-saving processes.
(2) A particular reaction (reaction specificity) takes place at the particular site (site specificity) of a compound of particular structure (substrate specificity) stereospecifically (stereospecificity). Therefore, no by-product is formed and a desired product can be obtained at a high yield and with a high purity.
(3) Since the substrate specificity of reaction is very high, only a desired compound can selectively be reacted even when various other compounds coexist. However, biocatalysts have the following drawbacks when used as they are. Since biocatalysts are generally water-soluble or otherwise used as an aqueous dispersion or in the presence of water, it is difficult to separate reaction products from raw materials, unreacted materials or biocatalysts used. Further, the catalytic activity of biocatalysts is lost by heat, organic solvents, acids and alkalies or even by reaction products. Thus, biocatalysts have been unable to fully exhibit their catalytic abilities.
Hence, research on biocatalyst immobilization by carrier has been conducted from around 1953. At present, the following four major methods are known for biocatalyst immobilization. (a) A bonding-to-carrier method wherein a biocatalyst is directly immobilized onto a insoluble carrier by covalent-bonding, physical adsorption, ionic-bonding or the like. (b) A crosslinking method wherein biocatalyst molecules are bonded with each other by a pclyfunctional reagent and made insoluble. (c) An enclosing method wherein a biocatalyst is enclosed in a lattice-shaped polymer gel, microcapsules, a liquid lipid membrane (liposome) or the like. (d) A combination method wherein at least two of the above method (a), (b) and (c) are combined appropriately.
Of these, an enclosing method using a polymer gel is thought to have the widest application because the method enables the immobilization of not only a single biocatalyst but also a plurality of biocatalysts. These conventional immobilization methods, however, have various drawbacks such as the following. The original activity of biocatalyst is reduced by immobilization; biocatalysts are not immobilized stably and a part of them dissolves out of a carrier; the reactivation of immobilized biocatalyst after use is difficult or impossible; the procedure for immobilization is complicated; and the precise immobilization of biocatalyst onto the desired sites of carrier is difficult.